The biological significance of double-stranded RNA (dsRNA) is reflected in the increasing evidence which indicates that dsRNA exerts regulatory functions in a wide range of eukaryotic biological systems including normal and tumor tissues, cultured cells, and cell-free extracts. Some of these effects include (1) the induction of interferon, (2) a cytotoxic effect on cells, (3) the suppression of tumor growth and development, (4) an enhancement of the immune response, and (5) the potentiation of inhibitory effects in cell-free extracts. One of the most distinctive effects of dsRNA is its capacity to promote an antiviral state in tissues and cells similar to that achieved by interferon. Significantly, treatment of cells with interferon causes the induction of several dsRNA-regulated components, two of which are potent inhibitors of protein synthesis. These are (a) a cAMP-independent protein kinase which phosphorylates the alpha-subunit of eIF-2, the protein chain initiation factor which activates initiator methionyl-tRNA; and (b) a (2-5A)n synthetase which polymerizes ATP into short oligonucleotides linked by (2'-5')-phosphodiester bonds of the form (pppA(2')p(5')A (2')p(5')A); these oligomers serve as activators of endonuclease activity. In addition to interferon-treated cells, the two dsRNA-regulated activities are found in normal and tumorigenic cells, and in reticulocyte lysates. The physiological roles of these functions are not clear. The induction of these two activities in interferon cells suggests that they are involved in the development of the antiviral state. The presence of the two activities in normal cells suggests that they are also involved in normal physiological processes. The primary objective of the proposed study is to determine the mechanisms by which dsRNA regulates macromolecular mechanisms with emphasis on the control of translation. The specific research goals will focus on the (a) isolation and characterization of the two dsRNA-regulated activities; (b) examination of their mechanisms of activation and expression; and (c) their physiological functions in normal, tumorigenic and virus-infected cells.